Steam generator having rotary tubular elements



Nov. 15, 1927.

J. V. BLOMQUIST ET AL STEAM GENERATOR HAVING- ROTARY TUBULAR ELEMENTS Filed May 15. 1925 f f J 0 a f i 4 m M/&W w W Jm@ W /x// W Patented Nov. 15, 1927.

UNITED STATES JOEAN VIKTOR BLOMQUIST AND KARL'FREDRIK WESSBLAD, OF STOCKHOLM, SWEDEN.

STEAM GENEBATOR HAVING ROTARY TUBULAR ELEMENTS.

Application filed May 15, 1925, Serial No. 30,548, and in Sweden June 30, 1924.

Steam generators comprising rotary tubular elements have generally been so arranged that the feed water is first fed into a fixed feed water pre-heater, in which it is heated up to the boiling point by combustion gases which previously have heated said tubular elements, and is then in this condition fed into the tubular elements where the evaporation takes place.

In generating steam having a pressure of about 100 atmospheres, for which purpose the said steam generators are especially suitable, the proportion of the evaporation heat to the heat of the liquid to be evaporated is such, that the combustion gases, after having transferred their heat to the steam generating tubular elements for the actual evaporation, still have sufficient remaining hoat to superheat the steam generated in the tubular elements and in addition to heat the feed water up to the boiling point, whereafter they are discharged into the chimney stack at a temperature of about 400 F. It may however occur that steam is also generated in the pre-heater on account of irregular firing. This quantity of steam, howeven is so small, that risk of damage to the tubes of the pre-heater when subjected to the hottest combustion gases is not present as 0 has been proved by actualexperiments.

The evaporation for each square foot of the steam generating tubular elements is about 82 pounds* at 100 atmospheres and could not be substantially sur-passed in constructions hitherto used. These tubular elements have hitherto been formed as smooth tubes with a diameter (of about 12 inches) the largest possible relation to the prevailing stresses of pressure and temperature, in order to reduce, as far as possible, the number of the same, as this portion of the steam generating plant is the most expensive one. It, under the supposition of a given heating value of the fire, the number of these tubular elements should be reduced to a number less than that hitherto used, then the temperature in. the furnace and thue the ,evaporation for each square foot of heating surface would obviously be increased. Hereby the combined stresses of pressure and temperature would also be increased, and to such an extent that the integrity of the device would be jeopardized and in addition the temperature of the combustion gases would thatmuch too great a quantity of steam be so high when reaching the fixed pre-heater would be generated therein, thereby endangering the pre-heater. v

The present invention discloses a device by means of which the disadvantages enumerated above are avoided in a most simple manner. The invention ,consists of tubular elements in the form of ribbed tubes, whereby the steam generation is considerably increased and an efiective cooling of the combustion gases is obtained, before these reach the pre-heater. I

` As mentioned above, the steam generation in a tubular element of 'about 12 inohes diameter and inch thickness of plate, is about 82 pounds per square foot an hour. The stress prevailing at the inner surface is then, on account of the inner pressure (100 atmospheres) and the stresses 'of temperature, about 32650 pounds' per square inch. As the limit of expansion strength of the material used for the tubular elements at the prevailing temperature is about 42500 Vpounds per square inch and as, in addition, there Wll be a negative stress at the external periphery, that is to say, a compression of about 7000 pounds per square inch, the safety against bursting is quite sufficient.

If, however. the boiler have tubes having a diameter of 9% inches and a thickness ot plate of 7 inch and be provided 'with ribs or flanges having an external diameter of 111 'inches with a sparing distance of inch between the center lines of the ribs, the evaporaton per square foot of heating surface exposed to the water may, under' the same stresses as before at the inner and outer circumference be increased to 154 pounds. the temperature of the combustion gases after thev have passed over the tubular elements also remaining the same as in the previous case.

Thus, it will be obvious that a considerable reduction is efiected in the number' of.

steam generating tubular elements necessary for a required steam generation. and consequently a reduction in the cost of the plant.

By this ineans it. will also be possible to advantageously produce similar steam gem erators adapted for a considerably lower pressure thanlOO atmospheres, which may be desirable in certain cases.

It is to be observed that the strength of the tubular elements is conditioned not only by the stresses due to the steam pressure but also by the stresses dueto the passage of heat throughthe material of the tubular elements. The latter stresses are increased in proportion to the thickness of the material. Therefore, given a certain steam pressure, a smooth tube having a certain thickness of material is not capable of transferring as much heat as a tube' of the same diameter but having less thickness of material and provided with ribs. These ribs increase the strength of the tube considerably and therefore it will be possible to produce such ribbed tubular elements with a less thickness of material than smooth tubes, which is of material importance not only with respect to the heat transfer but also as regards the costs of a steam generat'or of the type in question.

It is obvious that the total surface of the rotary tubular elements for a given' quantity of steam must be increased according as the steam pressure is lower, and this increase is in inverse proportion to the evaporation heat. If, therefore, a steam generator with rotary tubular elements is to be constructed for nstance for a pressure of atmospheres, then the surface of the tubular elements in comparison with a similar steam generator adapted for a pressure of 100 atmospheres, has to be increased in proportion of that is 1.32 times, in case the generating elements are formed as smooth` tubes, the figure 823 representing the evaporating heat at 30 atmospheres and 623 that at 100 atmospheres. By the provision of ribs or fianges on the tubular elements it is thus made possible to also produce` steam gene'ators having rotary tubular elements for comparatively low pressures, which otherwise, due to high costs, would be prohibitive.

The invention is illustrated by way of example in the accompanying drawing showing in section a steam generating plant. The plant comprises, a ribbed tubular element forming the subject. of this invention, a steam superheater, and a water pre-heater, it being understood, however, that for a. complete plant several of the just mentioned elements are necessary.but for the sake of clearness only one set of the elements is shown. The feed water is fed through a pre-heater in the form of' azig-zag tube l to the steam generating tubular elements 2, of which for the sake of clearness only one is shown, which elements are provided with fiange like extensions or ribs 3. By means of the toothed wheel 5 the tubular element 2 is, connected for instancewith an electromotor (not shown) and is rotated' by the latter at such a speed that the water contained in the tubular element, by the influence of the centrifugalforce, is evenly distributed over the peripheral nterior of the tubular element to form` a uniform. rotary layer of water therein. The steam is discharged from these tubular elements` 2' through a superheater 4 to the steam consumingapparatus and machines. The combustion gases at first strike the tubular elements 2, thereafter the superheater 4 and finally the feed' water pre-heater 1. only one embodiment of the steam generating device is illustrated, but it is obvious that the same may be varied without departing' from the scope of the nvention, the essential feature of the invention being the provision. of transverse or longitudinal flangelike extensions on the peripheral suraccs of the steam generating tubular elements for increasing the heating surface of the latter and increasing the evaporation per square unit of' the heating surface exposed to the water, while at the same time cooling the combustion gases, before they reach the pre-heater, to such an eXtent that an excessive steam generation in the latter cannot occur.

The flange like extensions may be formed in various ways. They may for instance consist of rings welded or shrunk on. F urther, they may be in the form of spirals of iron wound' on' the tubular elements and welded or shrunk thereon, or they may be formed by machining annular or spiral grooves in tubular elements having great thickness of plate, or by drawing the base material, so that longitudinal ribs are formed. It is obvious that the tubular elements can also be provided' with fiange like extensions or ribs of one 'kind or another at their peripheral nterior.

hat we claim as our* invention, and desire to secure by Letters Patent, is

A tubular' element rotatably supported adjacent its ends, means for rotating said element, the diameter of said element being so relatively large and the thickness of said walls being so relatvely slight' with respect to, standards of diameter and gage usually considered forthe temperature and pressnre to which it is designed to be subjected as a gene'ator, as to require strengthening means for said walls, and rings shrunk upon the peripheral' surface of said element.

In testimony whereof', we have signed our names to this specication.

JOHAN VIKTOR BLOMQUIST. KARL FREDRIK VVESSBLAD.

In the drawing i llU 

